The invention relates to a deformation member between a longitudinal member and a cross member of a motor vehicle, with the cross member having a horizontal central longitudinal plane which is vertically offset to the horizontal central longitudinal plane of the longitudinal member.
To satisfy the code for classification in a particular damage class of a motor vehicle insurance (e.g. according to the low-speed-test up to 16 km/h), the configuration of the front cross member system of a motor vehicle and especially the deformation members incorporated between the longitudinal member and the cross member are of particular importance. The deformation members should be so configured as to fully absorb loads encountered in the low-speed test and to rule out damage to the vehicle frame.
Optimum conditions for transforming impact energy in deformation energy exist in this context, when a deformation member is so configured and disposed as to form a quasi prolongation of a longitudinal member of the vehicle frame. This means in particular that the horizontal central longitudinal planes of the longitudinal member and the cross member extend in the same height level.
This ideal situation of a front cross member system of a motor vehicle is, however, oftentimes not present, when a motor vehicle, in particular a passenger car, is involved which has a weight of 2 tons or more. In these cases, the horizontal central longitudinal planes of the cross member and the longitudinal member are vertically offset to one another, primarily in such a manner that the central longitudinal plane of the cross member extends at a higher level than the central longitudinal plane of the longitudinal member. Upon introduction of impact forces into the cross member system, the vertical offset of the central longitudinal planes results in bending moments which adversely affect the deformation zone in the front portion. As a consequence, the cross member system has to be reinforced in order to absorb the bending moments. This, however, required heretofore comparably complicated and complex designs. These designs do not only lead to an increase in weight but also to higher productions costs.
U.S. Pat. No. 5,201,912 describes in this context a deformation element comprised of pipe portions and disposed between a longitudinal member and a cross member of a motor vehicle, with the cross member having a horizontal central longitudinal plane which is vertically offset to the horizontal central longitudinal plane of the longitudinal member. The pipe portions extend transversely within the cross member. In the event of a collision, the deformation members, supported by the longitudinal members, as well as the cross member itself should deform to convert the impact energy in deformation energy.
U.S. Pat. No. 5,785,367 discloses a deformation member at an end wall of the longitudinal member. This deformation member is substantially the cross member itself, with the cross member being traversed by an elongate U-shaped reinforcement member which is riveted to the box-like cross member.
U.S. Pat. No. 6,007,009 relates to the cross sectional configuration of cross members and the configuration of particular desired buckling areas which become effective in the event of a collision.
Finally, European Pat. No. EP 0 546 352 A1 discloses the application of welding joints as a classic joining method in automobile construction.
Based on the prior art, it is the object of the invention to provide a deformation member between a longitudinal member and a cross member, with the cross member having a horizontal central longitudinal plane which is vertically offset to the horizontal central longitudinal plane of the longitudinal member, wherein the deformation member is variable in design to allow easy adaptation to the respective type of vehicle and exhibits an optimum deformation behavior at slight weight while yet is easy to produce.
According to one aspect of the present invention, a deformation member is disposed between a longitudinal member and a cross member of a motor vehicle, with the cross member having a horizontal central longitudinal plane which is vertically offset to the horizontal central longitudinal plane of the longitudinal member, wherein the deformation member includes an elongate, hollow base body of polygonal cross section and a height which is greater than its width, and at least one reinforcing shell having U-shaped cross section and overlapping with the free longitudinal edges of its legs the base body in longitudinal direction of the base body and connected through welding to the base body via these longitudinal edges.
As central component of such a deformation element is an elongate, hollow base body of polygonal cross section and of a height which is greater than its width. Associated to this base body is at least one reinforcing shell having a U-shaped cross section and being dependent on the vehicle type involved, which reinforcing shell is so configured that the bending moments, encountered in the vertical central longitudinal plane as a consequence of the offset disposition of the horizontal central longitudinal planes of cross member and longitudinal member, are absorbed in an optimum manner. The reinforcing shell has legs whose longitudinal edges overlap the base body. The base body and the reinforcing shell are joined together by welding. Hereby, spot welding but also short longitudinal seams are sufficient for establishing a reliable connection. In particular the longitudinal edges are welded on the outside of the sidewalls of the base body. The extent of overlap of the legs with respect to the base body is determined by the respectively required deformation behavior. The base body and/or the reinforcing shell may be drawn or formed of compression molded parts. It is also possible to establish an optimal deformation behavior, even when the height-width ratio is very unfavorable, through variation of the sheet thickness in possible conjunction with the material (sheet steel and/or aluminum sheet). Hereby, in particular the transverse webs of the base body and the reinforcing shell are able to prevent the vertical legs of the base body and the reinforcing shell from collapse and the need for additional measures as a result of bead formation. The number of reinforcing shells to be associated to the base body in a quasi stack-like manner depends on the respective vehicle type and the deformation behavior. In any event, there is no need for additional mountings or reinforcing elements for compensating the height difference between the cross member and the longitudinal members. Still, the invention allows to reliably transform even great amounts of impact energy in deformation energy, because the deformation member can be supported not only by the longitudinal members but optionally also, for example, by the chassis subframe. The reinforcing shell can extend in precise parallel relationship to the base body or also in slanted relationship thereto. Moreover, the deformation behavior can be influenced by a different height of the legs of the reinforcing shell.
According to another feature of the present invention, the base body has a top and a bottom which are each embraced by at least one U-shaped reinforcing shell. In this manner, essentially three channels, arranged above one another, with a total of four cross webs are created as reinforcements.
The slanted disposition of the cross member confronting end walls of the deformation member realizes an even better force transfer from the cross member to the deformation member. The reason being the fact that not all areas of the end walls are impacted at a same time in the event of a crash, but initially only the corner zone neighboring the cross member, before the areas lying behind in the direction of a longitudinal member are deformed. Hereby, a slanted disposition of the end walls is conceivable in the vertical plane as well as in the horizontal plane. Further, a combined application of both configurations is possible.
When the deformation member is made up of a base body and two further reinforcing shells, it follows that in the event of a crash, for example, at first the upper reinforcing shell, then the base body and lastly the lower reinforcing shell are exposed to strain, and thus deformation is implemented with increasing resistance.
The base body may be formed in one piece from a drawn rectangular hollow section. However, to make the base body from two U-shaped shells which are joined together through welding via the longitudinal edges of their confronting legs. In this case, it is advantageous, when the longitudinal edges of a shell are inwardly recessed by about a sheet thickness so that the outer surfaces of top shell and bottom shell extend each in a vertical plane except for the overlap zone of the longitudinal edges.
A further advantageous embodiment of the invention to form the base body by a lower U-shaped shell and an upper trapezoidal shell. Also in this case, the longitudinal edges of the confronting legs of the shells are joined together by welding. As a consequence of the inclination of the cross web of the upper trapezoidal shell, the support of the vertical legs is not impaired. However, the added advantage is attained that the resistance increases even more uniformly over the length of the deformation member, when a force is introduced into the deformation member.
Finally, it is conceivable that the cross member confronting end walls of the base body and of each reinforcing shell are provided with a cover plate. The arrangement of the cover pate across the entire front cross section of the deformation member provides an additional improved force introduction from the cross member into the deformation member.